1) Field of the Invention
This invention relates to a wavelength multiplexing processing apparatus for use with a wavelength division multiplexing (WDM) system, and more particularly to a wavelength multiplexing processing apparatus which includes a combination of a waveguide optical system and a spatial optical system.
2) Description of the Related Art
The IP (Internet Protocol) network continues a worldwide high growth on the background of the increase in number of subscribers and the development of applications in the Internet. The demand for a transmission network which is an infrastructure of the IP network is increasing explosively. This tendency is exhibited conspicuously particularly in the North America of the IT (Information Technology) advanced countries, and communication undertakers progressively increase the investment in WDM (Wavelength Division Multiplexing) transmission systems and hasten the construction of optical networks which use the WDM transmission systems.
Examples of a network configuration of a WDM transmission system are shown in FIGS. 7(a), 7(b), 8(a) and 8(b). Referring first to FIG. 7(a), a plurality of ring networks are connected to each other (only two rings 801 and 802 are shown in FIG. 7(a)). A transmission apparatus 803 serving as a connection section between the rings 801 and 802 includes, as a wavelength multiplexing processing apparatus, for example, such a cross connect apparatus 900 for exchanging (that is, for cross connecting) optical signals of arbitrary wavelengths as shown in FIG. 7(b).
In particular, the cross connect apparatus 900 can exchange optical signals of arbitrary wavelengths for each other and includes, as shown in FIG. 7(b), multiplexing-demultiplexing processing sections 901 to 904 for performing a wavelength demultiplexing process for wavelength multiplexed optical signals propagating in the rings 801 and 802 and optical switches 905 for switchably outputting the wavelength demultiplexed optical signals of the different wavelengths from the rings 801 and 802 to the ring 801 or the ring 802.
For example, a wavelength multiplexed optical signal S1 circulating in the counterclockwise direction in FIG. 7(a) in the ring 801 and inputted to the transmission apparatus 803 is wavelength demultiplexed by the multiplexing-demultiplexing processing section 901 whereas another wavelength multiplexed optical signal S2 circulating in the clockwise direction in FIG. 7(a) in the ring 802 and inputted to the transmission apparatus 803 is wavelength demultiplexed by the multiplexing-demultiplexing processing section 902, and the output destination rings of the optical signals of the different wavelengths are switched by the optical switches 905. The output destination rings of the optical switches 905 can be set arbitrarily for the individual wavelengths.
It is to be noted that an optical signal to be outputted from any of the optical switches 905 to the ring 801 is wavelength multiplexed with the optical signals of the wavelengths by the multiplexing-demultiplexing processing section 903 and then signaled from the transmission apparatus 803 while an optical signal to be outputted from any of the optical switches 905 to the ring 802 is wavelength multiplexed with the optical signals of the other wavelengths by the multiplexing-demultiplexing processing section 904 and then signaled from the transmission apparatus 803.
FIG. 8(a) shows another configuration example of a network of a WDM transmission system. Referring to FIG. 8(a), an apparatus 806 is locally connected to a ring network 804 through a transmission apparatus 805. The apparatus 806 can extract an arbitrary wavelength signal propagating in the ring network 804 and simultaneously can place another optical signal of the same wavelength into the ring network 804 through an optical add-drop multiplexer 910 (FIG. 8(b)) provided in the transmission apparatus 805 and serving as a wavelength multiplexing processing apparatus.
FIG. 8(b) shows the optical add-drop multiplexer (OADM) 910 of the transmission apparatus 805. Referring to FIG.8(b), theoptical add-drop multiplexer 910 includes multiplexing-demultiplexing processing sections 911 and 912 for performing a wavelength demultiplexing process for wavelength multiplexed optical signals propagating in the ring network 804 and optical switches 913 capable of switchably outputting the wavelength demultiplexed optical signals of the different wavelengths from the ring network 804 to the ring network 804 or the apparatus 806.
For example, a wavelength multiplexed optical signal S3 circulating in the counterclockwise direction in FIG. 8 in the ring network 804 and inputted to the optical add-drop multiplexer 910 is wavelength demultiplexed by the multiplexing-demultiplexing processing section 911, and the output destinations of the resulting optical signals of the different wavelengths are switched to the ring network 804 or the apparatus 806 by the optical switches 913. The optical switches 913 can set the output destinations arbitrarily for the individual wavelengths.
Incidentally, as the cross connect apparatus 900 or the optical add-drop multiplexer 910 described hereinabove, such an apparatus as shown in FIG. 9 is conventionally known which is implemented using two arrayed waveguide gratings [AWG, refer to FIGS. 10(a) and 10(b)] (AWR1 and AWR2 in FIG. 9) (refer to Patent Document 1 hereinafter listed). In the apparatus shown in FIG. 9, a wavelength multiplexed optical signal is demultiplexed into a plurality of wavelength demultiplexed optical signals using an AWG and a transmission type planar diffraction grating and reflected by a two-dimensional array of mechanically tiltable micromirror switches 610 to perform optical add and drop.
In particular, optical signals having wavelengths to pass through the apparatus from among wavelength multiplexed lights incoming from an input (IN) port are reflected toward a lens 608 side so that they are outputted to a pass (PASS) port through an optical circulator 601 while optical signals having wavelengths to be dropped are reflected toward another lens 611 side so that they are outputted to a drop (DROP) port through another optical circulator 602. On the other hand, an optical signal to be added from an add (ADD) port is reflected to the lens 608 side so that it is outputted to the pass (PASS) port through the optical circulator 601.
Meanwhile, an apparatus which uses a diffraction grating together with tiltable micromirrors to perform optical add and drop is disclosed in Patent Document 2 hereinafter listed.
It is to be noted that also an apparatus disclosed in Patent Document 3 hereinafter listed is available as an apparatus which relates to the invention of the present application. However, the apparatus disclosed in Patent Document 3 involves neither optical add and drop process nor cross connect process.                [Patent Document 1]        Japanese Patent Laid-open No. 2000-347065        [Patent Document 2]        U.S. Pat. No. 5,960,133        [Patent Document 3]        Japanese Patent Laid-open No. Hei 11-95051        
However, the apparatus disclosed in Patent Document 1 has a subject to be solved in that, since it requires two AWGs and two optical circulators, a high cost is required for production of the apparatus and also in that, since it requires a great number of parts, the apparatus has a great size.
Meanwhile, the apparatus disclosed in Patent Document 2 is disadvantageous in that it cannot implement a cross connect function and it is difficult to implement an arrangement which is ready for an increase of the number of wavelengths to be multiplexed.